Antioxidant activities in holopelagic Sargassum species from the Mexican Caribbean: Temporal changes and intra-thallus variation

In the last decade, massive events of Sargassum influx have been reported causing ecological and economic damages. In this study, we evaluated the antioxidant potential of the holopelagic species S. fluitans, S. natans I, and S. natans VIII which arrived during 2018–2019 on the Mexican Caribbean coast. The monthly and intra-thallus variation of the total phenolic content (TPC) and antioxidant activity were determined in hydroethanolic extracts. The antioxidant potential was assessed using two free radical scavenging assays DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid) and FRAP as ferric reducing antioxidant power assay. All Sargassum species showed radical scavenging and reducing power due to their polyphenol content, but also due to the presence of other antioxidant metabolites such as mannitol, alginate, and fucoidan as observed in the ¹³C NMR spectra. The antioxidant capacity and the TPC in all Sargassum species were enhanced in August 2018 and March–April 2019, coinciding with elevated seawater temperatures and the highest solar irradiances. For all the holopelagic Sargassum species, the highest TPC was obtained in the axes rather than in the vesicles or leaves. These results suggest that invasive Sargassum biomass in the Mexican Caribbean contains different compounds with antioxidant properties and could be considered a natural alternative to synthetic antioxidants, especially if collected in the summer months.